Fluid operated clutch disengaging apparatus

ABSTRACT

A hydraulic clutch release system, particularly for motor vehicles has a master cylinder and a slave cylinder, and the slave cylinder has a piston  7  which is annular in form and works inside an annular cylinder  2 . The leading end of the cylinder is fitted with a seal  9  which is mounted on a one-piece seal carrier  10   a  through an undercut part of the carrier in which the seal fits without leaving any empty space.

The present invention relates generally to the hydraulic operation ofvehicle friction clutches, and more specifically to a hydraulicpiston/cylinder unit for use in a clutch operating system.

Clutch release systems having a slave cylinder as the central releasemember are known. They comprise a slave cylinder concentricallyenclosing a drive shaft and formed as a piston cylinder unit. Thecylinder can be detachably fixed on a gearbox housing. The piston can bea ring piston which is displaceable in a circular ring shaped pressurechamber of the cylinder, and the piston can be associated on thepressure chamber side with a seal which is fastened by a seal carrier onthe ring piston and is held in positive engagement in the seal carrier.

The invention also relates to a hydraulic piston/cylinder unit, whichmay be a slave cylinder for a hydraulic release system of a motorvehicle friction clutch (or may be a piston/cylinder unit for some otherapplication). The cylinder pressure housing can have a circular ringshaped pressure chamber with a ring piston displaceably guided in thechamber and an elastic seal fixed with keyed engagement on the ringpiston by means of a seal carrier.

The invention further relates to a hydraulic work cylinder which ispreferably formed as a component part of a release system for a shit andseparate clutch and may be mounted in a vehicle between an internalcombustion engine and a manual shift transmission. The release systemcan comprise a master cylinder unit operated by means of a pedal or anautomatic release unit and a pressure transfer mechanism to a furthercylinder, which is also to be called a slave cylinder, whichconcentrically surrounds a drive shaft which connects the internalcombustion engine to the transmission. The cylinder forms a pressurechamber which seen in cross-section is circular ring shaped and in whicha ring piston is guided axially displaceable between a bore wall of thecylinder and a guide sleeve concentric therewith. On the pressurechamber side the ring piston is associated with a seal.

A release system with the construction explained above is known from DE196 09 472 A1. The known release system is fitted with a seal carrierwhich is made without stock removal from steel. This support has on itsradially outer projection spaced from the free end a locking nose whichin the installation position engages with keyed engagement into a ringgroove or local recess of the piston. The locking nose which is shapedsemi-circular allows an automatic snap-fit engagement which can becomeloose by itself e.g. in the event of unfavourable manufacturingtolerances or ill-matched pairings. A seal carrier separated from thering piston leads to a breakdown or function failure or the slavecylinder. The internal profiled section of the seal carrier which servesto house and fasten the seal has according to the known release system arelatively large axial extension which has a direct detrimental effecton the guide length of the ring piston.

From the French Patent Application FR 2 730 532 on this subject a slavecylinder is known, more particularly for a hydraulic release system of afriction clutch of motor vehicles wherein for the positive lockingconnection of the seal on the ring piston a retaining plate is providedwhich is hooked by its ring-shaped part on the outer circumference ofthe ring piston by means of claws engaging in corresponding recesses andis anchored at the end side in the seal by a radially inwardly directedarea. Through this type of fastening a secure hold of the seal on theretaining plate is not guaranteed since the remaining cross-sectionalarea of the sealing material is now only small and can easily wear away.Furthermore the radial area of the retaining plate engages only from theoutside on the seal so that it is easy for the seal to cant.

From DE 34 39 652 A1 a slave cylinder is known for a hydraulic releasesystem of a friction clutch of motor vehicles wherein a stripper elementis provided between the ring piston and seal and engages from inside andoutside round the seal in dovetailed fashion and thus produces a fixedconnection with the seal whereby the stripper element only adjoins thering piston loose and the problem thereby exists that the contactbetween the ring piston and stipper element can be lost which leads tofunction failures of the slave cylinder. Play between the support facesof the seal and the sealing ring support reduces the stiffness and thusdegree of efficiency of the operating system associated therewith.

Furthermore from EP 0 168 932 A1 a hydraulic release device is knownhaving a further release shoulder. In order to obtain a surface whichfavours the wear behaviour of the sealing lips of the ring piston sealthe guide faces on the bore wall of the cylinder and on the guide sleeveare subjected to a special mechanical finishing treatment. By way ofexample the guide faces, i.e. the seal tracks can be enhanced bygrinding and/or polishing or honing. These processes extend themanufacturing cycles of the cylinder and are thus disadvantageous fromthe cost point of view.

For a specific surface treatment of the seal tracks it is generallyknown to subject these to a sand-blasting treatment in order to improvethe wear and/or sliding properties of the seal. By way of example theseal track can be enhanced in an aluminum cylinder by sand-blasting withglass balls. However such a process is very expensive and incurs highcosts.

Coating a sealing element can be concluded from DE 40 35 657 A1. To thisend in order to influence the sliding ability a foundation body ofelastomer can be coated with a material substance. By way of examplepolyvinyl chloride is used for the coating which is applied onto thefoundation body but does not however project into the marginal zone ofthe foundation body. Such a process is very expensive and demands highproduction quality. Manufacturing the foundation body and applying thecoating must thereby be carried out so that a definite wall thickness ofthe sealing lips is set in order to obtain for example the elasticityrequired for the sealing action.

The object of the present invention is therefore to provide a sealcarrier which:

ensures an effective permanent fixing on the ring piston;

allows improved support of the seal;

reduces the axial structural length.

The object of the invention is to avoid the faults of the knownsolutions and to provide a slave cylinder whose sealing assembly ensuresprecision guidance of the seal in the pressure chamber and furthermoreguarantees a permanent fixed connection of the seal relative to the ringpiston. Furthermore the seal carrier is to be capable of reliable massproduction and able to meet the demands regarding strength whilst takingup minimal axial structural space.

Starting from the technical faults of known solutions it is furthermorethe object of the invention to provide a seal for a hydraulic releasedevice.

which is optimised with regard to wear

whose service life is improved

whose friction is reduced and

which cuts down on noise.

Furthermore the release device is to be capable of economic production.

In a hydraulically operable release system of the kind in which a sealis secured on a ring piston by a circular, ring-shaped seal carrier, theobject of the invention is achieved by providing the seal with anundercut section that fits snugly into the seal carrier without formingany gaps.

An advantageous embodiment, has a seal carrier with different wallthickness. Starting from the greatest wall thickness in the area of theouter axial projection according to the invention the wall thickness isprovided with a reduced thickness in other sections of the seal carrier,more particularly in partial areas of the internal profiled section oropening directed towards the seal. The proposed difference in wallthicknesses takes into account the manufacturing process, i.e. thedeep-drawing process which is preferably used allows the seal carrier tobe designed with the optimum profile determined for example byFE-calculation (finite elements). At the same time the seal carrieraccording to the invention allows optimum axial structural length andshaping which ensures a cost-effective production.

The invention furthermore included an enlarged end face of the sealcarrier on the seal side. To this end the rounded transition between theend face and the inner or outer axial projection of the seal carrier isdesigned so that the sections of the end faces or the axial projectionsintersect as a secant the curve formed by the radii at the transitions.This geometric design of the seal carrier enlarges the support face forthe seal which has an advantageous effect on the service life of thesealing ring. According to the invention in each rounded transition zonebetween the end face and the axial projection of the seal carrier it isproposed that starting from the end face an at first smaller radius isadjoined by a larger radius. This measurement increases each time theend face and allows a more heavily rounded end-side transition to thesleeve face of the axially aligned projections of the seal carrier. Aseal carrier formed in this way avoids or reduces a gap extrusion of thesealing material between the seal carrier and seal track. At the sametime the shear tension in the seal is reduced in the area of the supporton the end sides of the seal carrier.

A flanged section provided at the free end of the outer axial projectionserves to fasten the seal carrier. In the installation position of theseal carrier the flanged section is angled inwards to produce a radialoverlap with a sleeve structure of the ring piston. The flanging canthereby provided round the entire circumference or partially.

A definite overlap in the area of the undercut sections is provided forthe internal profiled section of the seal carrier according to theinvention provided for fastening the seal. A measurement H≧0.1S₁ isprovided for the at least one-sided radial overlap. This overlap makesit possible when installing the seal for the sealing material to fillout the internal profiled section of the seal carrier at leastsubstantially and thus for the seal to receive a permanent hold.

One advantageous development of the invention provides a ring pistonwhich is provided on the pressure chamber side with a shoulderprotruding axially from the end side. This shoulder on the insideadvantageously increases the guide length of the ring piston on theguide sleeve. The shoulder is thereby formed so that this contacts theseal carrier neither radially nor axially.

To achieve the optimum axial structural length of the seal carrieraccording to the invention a spacing measurement L₁ is determinedbetween the end side and the planar surface of the seal carrier whichcorresponds to >3.5 times the value of the wall thickness S₁. Sealcarriers with small spacing measurements defined in this way allow adesired extended axial guide length of the ring piston which has anadvantageous effect on the function of the slave cylinder.

An advantageous development of the invention proposes designing the sealcarrier so that a doubled or folded area adjoins the lead-in zones ofthe opening. As a spacing measurement for a seal carrier designed inthis way a measurement is provided between the end side and the planarsurface of the seal carrier which corresponds maximum to 3.5 times thevalue of the wall thickness S₁. A seal carrier with a doubled areapreviously explained consequently allows the axial structural length ofthe seal carrier to be further reduced.

For the wall thickness S₁ of the seal carrier in the outer axialprojection a measurement of greater than 0.2 mm has proved practical andexpedient. A seal carrier with this wall thickness allows acost-effective production which can be made without stock removal andnevertheless has sufficient strength.

The configuration of the seal carrier according to the inventionfurthermore includes an internal profiled section mounted centrally inthe circular ring shaped end face of the seal carrier. This internalprofiling ensures in the case of a seal biased with pressure that theaxial force introduced from the seal onto the seal carrier istransferred in a straight line to the ring piston. For groove ring sealsused having asymmetrically arranged sealing lips the invention likewiseincludes a seal carrier whose axis of symmetry (S_(a)) from the internalprofile for holding the seal is arranged coinciding with or off-set fromthe end-side centre (M) of the seal carrier.

In the rounded transition zone between the end face and at least oneaxial projection of the seal carrier it is proposed according to theinvention that starting from the end face an at first smaller radius isadjoined by a larger radius. This measurement enlarges each time the endface and allows a more heavily rounded end-side transition to the sleeveface of the axially aligned projections of the seal carrier whereby adesired smaller edge radius is set which reduces a gap extrusion of thesealing material.

A further advantageous design of the invention provides a seal carrierhaving a symmetrically shaped internal profile which has two undercutsections. Deviating from this the invention likewise includes sealingsupports with only one undercut section which can be aligned in thedirection of the outer projection or towards the inner projection. Theinvention further includes undercut sections of different geometricshape in an internal profile which can be determined for example independence on the material pairing of the seal carrier and/or seal or onother parameters.

The seal carrier according to the invention having multi-curved shapingis provided in the individual transitions with differently shaped radii.Fixing the radii in this way serves on the one hand to enlarge theend-side support surface of the seal on the seal carrier and tofacilitate the elastic deformation of the sealing substance for fittinginto the opening or internal profiled section of the seal carrier and onthe other to simplify the manufacture of the seal carrier. In the areaof the lead-in zone of the seal carrier the radii thereby exceed themeasurement of the wall thickness S₁. The inner radii in the internalprofiled section or mounting of the seal carrier are ≦ the radii at thelead-in zone.

The idea of the invention furthermore includes an overall length of theouter axial projection which is greater than the distance measurementbetween the end side and the planar surface of the seal carrier. Theaxial projection can thereby be adapted to the relevant conditions orrequirements relating to the shape of the ring piston and the type offastening.

The idea of the invention provides a ventilation groove in the sealcarrier for the purpose of improving the seal assembly. The air includedin the internal profiled section can escape through the seal groove whenmounting the seal and thus the internal profiled section can becompletely filled out with sealant material. A ventilation groove isthereby preferably provided which is formed axially parallel to theouter projection in a protrusion of the seal carrier. Alternatively theseal carrier can be provided for ventilation with a bore which ispreferably formed in the planar surface.

A further development of the seal carrier provides that the innerprojection is guided up to the end face of the ring piston whilstmaintaining an annular gap. For ring pistons which are provided on theend side with an axially protruding shoulder by which the guide lengthof the ring piston on the guide sleeve can be increased, the innerprojection of the seal carrier is correspondingly shortened so that anannular gap is likewise set between the shoulder of the ring piston andthe projection. For further optimising the guide length of the ringpiston its axially protruding shoulder can be guided up to the radiallyaligned section of the seal carrier. The inner projection of the sealcarrier is thereby omitted. To avoid contact or support of the sealcarrier on the shoulder of the ring piston an axially and radiallysetting annular gap is provided between these component parts.

For the inner projection of the seal carrier the invention proposes thatthis runs conical at least in part.

Starting from the end side of the seal carrier towards the free end, theinner projection is directed radially outwards. This design preventsdetrimental contact of the guide sleeve by the free end of theprojection. The design of the inner projection according to theinvention further proposes that in the installed state the projection isguided up to the end side of the ring piston whilst maintaining anannular gap. The annular gap for which a measurement of ≧0.1S₁ ispreferably provided creates a controlled seal carrier which is supportedon the ring piston solely through the planar surface.

According to the invention a metal material capable of being deep drawnis provided as the material for the seal carrier which is made withoutstock removal. A steel plate St4 or a comparable material is a suitableexample.

The object of the invention is further achieved in that the seal carrierhas a circular ring shaped mounting chamber opening towards the seal andprovided with an inner ring and outer sleeve, that the inner space inthe end area of the mounting chamber facing the seal is reduced, thatthe seal has at least a correspondingly shaped recess, ring groove orthe like for keyed connection with the seal carrier and that the sealcarrier is constructed of two component parts which can be madeseparately from each other. It is thereby ensured on the one hand thatthe seal is fixedly anchored in the seal carrier and is enclosed by theinner ring and/or outer sleeve of the circular ring shaped mountingchamber wherein the seal is not weakened in cross-section to the extentthat it can rip or tear. The invention reduces the axial and radial playbetween the sealing ring and sealing ring support and at the same timeimproves the stiffness and degree of efficiency of the overall system.In that the seal carrier consists of two parts these individual partscan on the other hand be easily manufactured so that overall acost-effective seal carrier is produced.

The reduction in the internal spacing in the end area can be formed bothby a restriction on the other sleeve and a widening of the diameter onthe inner ring whereby both measures can also exist. In order to avoidsharp edge transitions in the case of the restriction or diameterexpansion these are provided in the form of ring beads. Correspondingdeformations on the seal also produce suitably rounded transitionsthere.

The two-part construction of the ring support is preferably designed sothat the outer sleeve is formed circular ring shaped and that insidesame is the inner ring which is adjoined on the side remote from theseal by a disc-like flange which is in active connection with the outersleeve.

This active connection can be made on the one hand so that the disc likeflange is fixed in a fixing groove on the inner circumference of theouter sleeve. This is particularly advantageous when the outer sleeveand inner ring are made of a material having sufficient elasticdeformability whereby then the disc-like flange is pressed into theouter sleeve and snap-fits in the fixing groove. Various materials canbe used such as for example steel, aluminium, sintered parts or plasticsparts whereby the latter can also be strengthened by steelreinforcements.

The disc-like flange can also have on its outer circumferenceprojections which project into windows or recesses on the outer sleeve.Also with this design the disc-like flanged can be pressed into theouter sleeve whereby the projections snap-fit in the windows or recesseson the outer sleeve.

In a further development of the invention the disc-like flange can alsobe fixed in one direction on one or more stops on the inside face of theouter sleeve and can be fixed on the opposite side by material embossingor welding. The disc-like flange can thereby also be stuck to the outersleeve. With plastics parts fixing the disc-like flange can be achievedby ultrasound welding whereby in the case of metal parts laser weldingor soldering in a continuous furnace can also be used. Both the outersleeve and the inner ring can if they are made of aluminium or steelalso be formed as flow pressed parts. The or each stop can be producedby rolling or embossing, particularly if the outer sleeve is made ofsteel, whereby the disc like flange can also be connected non-detachableto the stops directly e.g. through spot welding or through resistancewelding.

The disc like flange can be fixed on the outer sleeve according to afurther design of the invention where after installing same the outersleeve receives grooves, projections, studs or the like by rolling orimprinting each side of the disc like flange.

Also the disc like flange can be fixed by one or more stops, byprojections, studs and the like on the inner circumference of the outersleeve on one side and by the end face of the ring piston on the othersince the outer sleeve clamps the disc-like flange along with samethrough its keyed fastening on the ring piston.

The disc like flange can finally be provided on its outer circumferencewith a thread and can be screwed onto a counter thread on the innercircumference of the outer sleeve.

The outer sleeve in turn has at its end area remote from the sealinwardly directed projections, studs or the like which can hook withkeyed engagement into corresponding recesses, undercut sections or aring-shaped restriction on the ring piston.

A further alternative fastening of the inner ring on the outer sleeve isprovided in that the disc like flange has on its outer circumference asubstantially cylindrical extension which extends in the directionremote from the seal and corresponds with the inner circumference of theouter sleeve whereby the cylindrical extension is fixed on the innercircumference of the outer sleeve by adhesive, welding or press-fit. Thecylindrical extension can also have windows or openings which correspondwith the inwardly directed projections on the outer sleeve so that theseundertake both the fixing of the cylindrical extension whilst ensuringthe fastening on the outer circumference of the ring piston.

The problem previously mentioned is further solved according to theinvention by a seal which is subjected at least in part to chemicalfinishing. Particularly suitable for this are halogens though which amarginal zone of the sealing substance can be chemically changed.Halogens are characterized by a large reaction capacity which can betransferred to materials from which seals are made.

Advantageously by a chemical halogen treatment of the seal it ispossible to achieve a purposeful hardening or brittleness of a marginalzone of the seal. The chemical treatment which is also termedhalogenization signifies the introduction of halogen into an organiccompound for example into a benzene ring. The bearing proportion of thesealing lips can be directly influences by the changed materialproperties for example. By including the special material properties ofthe relevant sealing material used each time and taking into account thedifferent reactions it is possible to change or influence by differentparameters the depth of penetration of the marginal zone of the seal. Asa result of the chemical treatment according to the invention whichinfluences the bearing proportion of the sealing lips, on the one handthe sealing quality of the seal is improved and on the other the sealinglip becomes more resistant to wear as a result of the brittle finish orsurface hardening. Furthermore the chemical treatment reduces thefriction force so that the release force required to operate the shiftand separate clutch is clearly reduced independently of the temperatureof the release system. Finally the seal according to the inventionreduces the noise development as a result of clear friction conditions.As a result of the brittle condition the disadvantageous stick-slipeffect which is linked with a corresponding noise development is nowavoided. The effect also designated back-slipping leads in shortintervals periodically to sticking, breaking loose and further movementof the sealing lip on the sealing track face.

Advantageously through the invention the micro deformation of thesealing material in the area of the sealing lip is reduced whereby thefriction can be directly reduced. The chemical finishing treatment inconjunction with the optimized geometry of the seal leads to a solutionto the problem on which this invention is based. As a result of thechanged shaping a reduced contact length of the seal is set and thus ashortened dynamic cylindrical contact surface of the sealing lips inorder to minimize the friction. The optimized sealing geometry accordingto the invention creates overall a shortened seal which allows anincreased stroke of the ring piston or optimisation of the structuralspace in the axial direction of the cylinder.

As a cost-improving measure the invention proposes restricting thechemical finishing treatment to the sealing lips of the seal. To thisend a fluid is preferably used in which halogens are dissolved.Deliberately immersing the seal can consequently result in a localchemical change of the marginal zone. The hardening or brittle naturedesired for the sealing lip is thus not transferred to the remainingareas of the seal.

In a further development of the invention it is proposed for thechemical finishing treatment to chlorinate, brominate, iodinate orfluorinate the seal or partial areas of the seal. This finishingtreatment can also be carried out in a gaseous or liquid phase and islikewise suitable for the materials normally used for seals, such ase.g. EPDM. Processes normally used in the chemical industry are used forthis purpose. With a fluorinated sealing lip an effect is set whereinthe sealing lip remains relatively elastic and has a sufficient sealingaction from fluids but allows gas to pass through the sealing lip to alimited amount. Chlorination is used in particular to achieve a relativestiffening of the sealing lip but here a reduced sealing friction is setcompared with a fluorinated sealing lip.

The chemical finishing treatment changes the marginal zone in that forexample chlorine or another halogen diffuses into the sealing substanceand thereby influences the marginal zone to a depth of >5 μm.

For the hydraulic release device different pairings of material areprovided between the seal, i.e. the sealing lips thereof and the sealtracks on the bore wall of the cylinder and guide sleeve. Preferably anelastomer such as EPDM, HNBR, NBR, is provided as the sealing material.A metal material, more particularly aluminium is provided as a suitablematerial for the cylinder. The guide sleeve which is integrated in thecylinder represents however a sheet metal part which is made withoutstock removal by the deep-drawing process.

A bearing proportion of >15% is provided for the surface quality of thesealing track on the bore wall of the cylinder. The sleeve face of theguide sleeve on which the inner sealing lip of the seal sealinglyadjoins has however a bearing proportion of >20%.

The structure of the release system according to the inventionfurthermore has an asymmetrically shaped seal with sealing lips whoselongitudinal extension and wall thickness differ from each other. Theinner sealing lip has a greater length extension than the outer sealinglip. On the other hand the wall thickness of the outer sealing lipexceeds the wall thickness of the inner sealing lip.

For an optimum design of the seal a wall thickness ratio of the outersealing lip to the inner sealing lip of $\frac{L_{6}}{L_{5}} \geq 1.1$

has proved advantageous. For the longitudinal extension of the sealinglips a length ratio $\frac{L_{1}}{L_{3}} \geq 1.1$

between the inner sealing lip to outer sealing lip has proved optimum.

The further development of the seal comprises a V-shaped ring groove onthe end side restricted radially by the sealing lips. The groove depthis thereby defined by a measurement which extends from the back of theseal to the groove base. According to the invention it is establishedthat this measurement always exceeds a length measurement from the backof the seal to a function point of the inner sealing lip.

The device of the seal according to the invention further includes theshaping of an outer contour of the inner and outer sealing lip.According to this each sealing lip in the non-installed state intersectsan active line corresponding to the sealing lip track face in theinstallation position on the bore wall of the cylinder or on the sleeveface of the guide sleeve. Starting from the back of the seal the outercontour of the two sealing lips defines on the inside an underlap zoneB;D extending up to the active line. After the intersection of thesealing lip outer contour with the active line the outer contours of thetwo sealing lips define on the outside an overlap zone A;C. The overlapzones A;C thereby each extend from the intersection with the active lineup to a function point at which each relevant sealing lip adjoins thesealing track with the greatest radial pretension.

The following surface area ratios can be designated optimum for eachrelevant sealing lip. For the inner sealing lip a ratio of overlap zoneA to underlap zone B is $\frac{A}{B} > 0.5$

and for the outer sealing lip a corresponding ratio is provided of$\frac{C}{D} > {0.7.}$

As an alternative to the surface area ratios mentioned above theinvention also includes a surface area ratio of $\frac{A}{B} = 1$

as well as a matching surface area ratio $\frac{C}{D} = 1.$

Furthermore the seal can have matching surface area ratios${\frac{A}{B} = \frac{C}{D}},$

i.e. the surface areas of the overlap zones and underlap zones have thesame size.

The design of the seal further includes a measurement ratio which is setbetween a vertical measurement—which determines the radial spacingbetween the active lines of the two sealing lips—and a lengthmeasurement between the back of the seal and the free end of theradially inner sealing lip. This measurement ratio$\frac{L_{1} + L_{4}}{D_{1}}$

is to amount to >0.6.

In order to determine the length measurements of the two sealing lips,starting from the back of the seal to the function point, the followinglength measurements are provided: for the inner sealing lip a lengthmeasurement of >2.6 mm is provided, characterised by L₁. Thecorresponding length measurement for the radially outer sealing lip,designated L₃, amounts to >2.2 mm.

The two sealing lips each form, starting from the function point, an endsection whose outer contour in the non-installed state runs at an angleof ±5°.

The depth of the V-shaped circumferential groove formed at the end sidein the seal is determined by a measurement ratio which is related eachtime to the back of the seal. The measurement L₁ between the back of theseal and the function point of the inner sealing lip set in relation tothe measurement L₂ between the groove base of the ring groove at the endand the back of the seal amounts to >1. This measurement ratio preventsthe seal from becoming weakened in the area of the sealing lip root.

According to a further development of the invention each sealing lip isprovided on the outer contour in the area of the function point with aradius R₁; R₂. Thus a rounded transition is set in the area of thefunction point between the substantially cylindrical end section and theouter contour of the seal running towards the back of the seal.

For the V-shaped ring groove of the seal according to the invention itis proposed that this forms a radius R₃ at the groove base. The size ofthe radius R₃ is thereby selected so that this exceeds the radius R₁;R₂.

The invention further proposes a rounded transition from the outercontour of the relevant sealing lip to the back of the seal. Thistransition is likewise designed in the form of a radius R₄; R₅ whereinthese radii are larger than the radii R₁; R₂. The radii R₄; R₅ can bedimensioned both different from each other or the same size.

For the partial chemical finishing treatment of the seal it is proposedthat each relevant sealing lip is biased in the area of the outercontour each time starting from the tangent point of the radius R₄; R₅to the back of the seal up to the free end.

The chemical finishing treatment of a sealing substance according to theinvention can be used quite generally for seals in vehicle hydraulics.Both seals which are used in a master cylinder and seals for a mastercylinder can be subjected to a halogen treatment where necessary.

The invention will now be explained in further detail with reference tothe 30 figures in which:

FIG. 1 is a half-sectional view of a ring piston on which a seal carrieraccording to the invention, including a groove ring seal, is fastened;

FIG. 2 is a view substantially according to FIG. 1 wherein the ringpiston, in order to receive an increased guide length, is provided witha shoulder which interacts with a corresponding inner projection of theseal carrier;

FIG. 3 shows a ring piston further improved with regard to its guidelength compared with FIG. 2, with a suitably adapted seal carrier;

FIG. 4 shows in an individual itemised drawing a longitudinal sectionthrough the seal carrier shown in FIG. 1;

FIG. 5 shows an alternative form of seal carrier which has a doubledarea in order to shorten the axial structural length;

FIG. 6 shows on an enlarged scale the flanged area arranged at the endside on the outer axial projection of the seal carrier and engaging overthe stepped area of the ring piston;

FIG. 7 shows a cut-out section of the seal carrier shown in FIG. 4 andhaving a ventilation groove and a ventilation bore;

FIG. 8 is a front view of the area of the seal carrier shown in FIG. 7;

FIG. 9 is an individual itemised drawing of a seal carrier having anasymmetrically shaped inner profile provided with an undercut sectiondirected towards the inner projection;

FIG. 10 shows an individual itemised drawing of a seal carrier whoseinner profile has an undercut section directed towards the outerprojection;

FIG. 11 shows the construction of a seal carrier with a symmetricalinner profile and the omission of the inner projection;

FIG. 12 shows a slave cylinder, installed in a hydraulic release systemof a friction clutch of motor vehicles;

FIG. 13 shows the detail X of FIG. 12 on an enlarged scale;

FIG. 14 shows the view according to FIG. 13 with an alternative designof the seal carrier;

FIG. 15 shows the seal carrier according to FIG. 13 with an alternativefastening of the flange on the outer sleeve of the seal carrier;

FIGS. 16 to 26 show alternative designs of the seal carrier;

FIG. 27 is a semi-sectional view of a hydraulic release system accordingto the invention;

FIG. 28 is a longitudinal sectional view of the profile of the seal onan enlarged scale;

FIG. 29 is a diagram showing the pedal force curve of release systemsknown up until now and

FIG. 30 shows the pedal force curve for a release system according tothe invention.

FIG. 1 shows some component parts of a hydraulically operable releasesystem 1 in semi-section. The release system 1 comprises a pressurehousing 2 which is arranged concentric with a drive shaft 3 whichconnects an internal combustion engine to a manual shift gearwheeltransmission. A guide sleeve 6 arranged radially spaced from both a borewall 4 of the pressure housing 4 and from a drive shaft 3 forms a sleeveface 5 on which the ring piston 7 is guided. The ring piston 7 is sealedfrom a pressure chamber 8. A seal 9 serves for this which is fastenedwith keyed engagement on the ring piston 7 by means of a seal carrier 10a. The seal 9 which is formed as a groove ring seal sealingly adjoinsthe guide sleeve 6 by its radially inner sealing lip 11. The radiallyouter sealing lip 12 is however guided sealingly on the bore wall 4. Theseal carrier 10 a which is formed from sheet metal without stock removalforms on the seal side an end-side opening 13 which is widened outradially in the direction of the ring piston 7 and thereby forms atrapezoidal inner profile 14. In the installation position of the seal 9the inner profile 14 is filled up with sealant material of the seal 9 inorder to produce a positive-locking fastening of the seal 9 on the sealcarrier 10 a. An outer axially protruding projection 15 which startingfrom an end side 20 a engages concentrically on the outside round anend-side section of the sleeve face 16 of the ring piston 7 serves asfastening for the seal carrier 10 a on the ring piston 7. At the freeend the projection 15 is provided with a flanged area 17 at the step 18directed radially inwards at a right angle.

In order to achieve a play-afflicted bearing of the seal carrier 10 aagainst the ring piston 7 the projection 15 is attached to the ringpiston 7 with an axial play x as well as with a radial play y. On theside directed towards the guide sleeve 6 the seal carrier 10 a forms afurther projection 19 a which runs conical starting from an end side 20b of the seal carrier 10 a so that a free end of the projection 19 adoes not contact the guide sleeve 6. In FIG. 1 the seal carrier 10 a issupported by a planar surface 21 on an end face 22 of the ring piston 7.In this position of the seal carrier 10 a an annular gap z₁ is formedbetween the free end of the projection 19 a and the end face 22 of thering piston 7 to prevent the projection 19 a from contacting the ringpiston. Through this measure it is ensured that in the event of pressurebiasing of the seal 9 force is introduced onto the ring piston 7 solelythrough the planar surface 21 of the seal carrier 10 a on the end side22 of the ring piston 7.

In a second and third embodiment (FIGS. 2 and 3) of a hydraulicallyoperable release system 1 the component parts agreeing with the firstembodiment are provided with the same reference numerals so thatreference can be made to the description of the first embodiment toavoid repetitions.

In FIG. 2 the ring piston 7 provided on the pressure chamber side with ashoulder 30 axially emerging from the end face 22 and with which theguide length of the ring piston 7 on the guide sleeve 6 can beincreased. The inner projection 19 a is shortened accordinglycorresponding to the length of the shoulder 30. In order to avoid theprojection 19 a contacting or bearing against the shoulder 30 an axialplay is provided between these component parts, characterised by z₂. Thedesign of the shoulder 30 furthermore provides a radial play relative tothe seal carrier 10 a which agrees with the radial play Y between theouter projection 15 and the ring piston 7.

FIG. 3 shows the ring piston 7 with a further optimized guide length. Tothis end the ring piston 7 is provided at the end side with a shoulder31 which extends whilst maintaining an annular gap Z₃ up to the radiallyaligned area of the seal carrier 10 a designated the end side 20 b. Asalready explained with reference to FIG. 2 the shoulder 31 also runs upto the seal carrier 10 a whilst maintaining the radial play Y.

FIG. 4 shows the exact construction of the seal carrier 10 a accordingto the invention. By way of example different wall thickness areprovided for the seal carrier 10 a. This means that starting from a wallthickness S₁ in the area of the outer axial projection 15, a reducedwall thickness S₂ is permissible for example in the area of a lead-inzone 23 a and/or a wall thickness S₃ is permissible in the area of theplanar surface 21 as well as the wall thickness S₄ in the area of theend side 20 b. In addition to the areas of the seal carrier 10 apreciously mentioned outside of the projection 15 any other types ofsections of the seal carrier with a wall thickness differing from thewall thickness S₁ can also be provided, depending on the strengthrequirements and as a consequence of the manufacturing process used. Theshaping of the seal carrier 10 a furthermore provides following radii inthe area of the rounded transitions. In the transition area from the endside 20 a to the sleeve face of the projection 15 the end side 20 a isadjoined by a first radius R₁, followed by a further larger or similarsized radius R₂. For the transition beginning from the end side 20 bfirst a radius R₃ is provided which is adjoined by a similar or largerradius R₄ in the transition to the projection 19 a. For the radii R₁, R₃a measurement of <0.8 mm is provided. In the lead-in zones 23 a, 23 b ofthe sealing ring support 10 a, i.e. beginning from the end side 20 a, 20b in the direction of the inner profile 14 a radius R₅, R₆ is providedwith a measurement > the wall thickness S₁. In the inner profiledsection 14 of the seal carrier 10 a at the end of the planar surface 21a radius R₇ and R₈ is provided respectively which are designed ≦ theradii R₅, R₆.

The seal carrier 10 a has in the area of the inner profile 14 an overlapH which corresponds to half the measured difference between the opening13 and an expanded measurement Sp of the inner profile 14. A measurementof >0.1S₁ is provided for the undercut section H which is also to betermed the radial overlap. FIG. 4 shows a radial stagger between theaxis of symmetry Sa of the inner profiled section 14 and a centre M ofthe seal carrier 10 a. The essential measurement of the seal carrier 10a directly affecting the axial structural length of the ring piston 7 isthe spacing measurement L₁ which extends from the end side 20 a, 20 b upto the planar surface 21. The measurement L₂ determines the length ofthe outer projection 15. The measurement L₃ determines the longitudinalextension of the projection 15, reduced by the measurement for a flangedstep 24.

With the further embodiment shown in FIG. 5 of the seal carrier 10 b theareas agreeing with the first embodiment (FIG. 4) are provided with thesame reference numerals so that reference can be made to the descriptionof the first embodiment in order to avoid repetition. Differently fromthe seal carrier 10 a the seal carrier 10 b has a differently shapedinternal profiled section 26. Each lead-in zone is adjoined by a doubledarea 25 a, 25 b which forms a length-restricted section of the sealcarrier 10 b running parallel to the end side 20 a, 20 b. The doubledarea 25 a, 25 b engenders a reduced axial length of the internalprofiled section 26 which has a direct effect on the measurement L₁ aswell as on the remaining length measurements L₂, L₂ of the seal carrier.

FIG. 6 shows on an enlarged scale the free end of the outer axialprojection 15 of the seal carrier 10 a, 10 b. As an alternative to FIG.1 the flanged step 24 is angled inwards not at right angles, but at anangle of about 45 degrees.

FIG. 7 shows a further feature according to the invention on the sealcarrier 10 a. The lead-in zone 23 a is accordingly provided with aventilation groove 29 which runs parallel to the projection 15 andthrough which when pressing the seal 9 into the seal carrier 10 a theair included in the internal profiled section 14 can escape. Theposition and shaping of the ventilation groove 29 can be seen from FIG.8 which is a front view of the section of the seal carrier 10 a shown inFIG. 7. In addition or as an alternative to this the seal carrier 10 acan be provided with a ventilation bore 32 which is formed in the planarsurface 21.

FIGS. 9 to 11 show further variations of the seal carrier depicted inFIG. 4. The areas of the seal carrier agreeing with FIG. 4 are providedwith the same reference numerals. The following descriptions relate todifferent designs of the seal carrier.

FIG. 9 shows the seal carrier 10 c whose internal profiled section 27 isshaped asymmetric. As opposed to the internal profiled section 14according to FIG. 4 here the internal profiled section 27 has only oneundercut section directed towards the inner projection 19 a, andcharacterised by H.

The seal carrier 10 d according to FIG. 10 is likewise provided with anasymmetrically shaped internal profiled section 28. The internalprofiled section thereby forms an undercut section H which is directedtowards the outer projection 15. Common to both inner profiled sections27, 28 according to FIGS. 9 and 10 is an axially aligned area oppositethe undercut section H.

FIG. 11 shows the seal carrier 10 e which is shown in FIG. 3 in theinstalled position. This seal carrier 10 e is provided with asymmetrically shaped internal profiled section 14, corresponding to theseal carrier 10 a according to FIG. 4. As a difference here the sealcarrier 10 e has no inner axial projection 19 a. Rather the internalprofiled section 14 is adjoined by a radially aligned end side 20 b.

In FIG. 12101 designates a release system which is shown insemi-section. The release system 101 comprises a pressure housing 102,which is mounted coaxial with a drive shaft 103 which connects forexample an internal combustion engine to a shift transmission. Thepressure housing 102 is thereby fastened on a gearbox housing 104. Thepressure housing 102 has a guide sleeve 105 which is in sealingconnection with a housing flange 106 and forms a pressure chamber 107which is formed circular ring shaped. A ring piston 108 is guided in thepressure chamber 107 and is in active connection with an inclinedshoulder bearing which has in turn a support face 109 through which therelease mechanism (not shown) of a friction clutch (likewise not shown)can be operated.

Where shown in detail in FIGS. 13 to 23 the reference numeral 110designates the seal which is held in a seal carrier 111. The sealcarrier 111 has an inner ring 112 which is mounted inside an outersleeve 114 through a disc-like flange 113. The inner ring 112 has a ringbead 15 through which the circular ring shaped mounting chamber 116 (seeFIGS. 14 to 20 and 22) receives in its end area a reduced spacing whichapart from FIG. 110 is reduced still further by an inner ring bead 117on the outer sleeve 114 so that the seal 110 is held in positive lockingengagement by its inside and outside. The outer sleeve 114 has at itsend area remote from the seal 110 projections 118 which hook with keyedengagement on the ring piston 108 by undercut sections 119.

FIGS. 13 to 26 differ substantially from each other in that thedisc-like flange 113 is secured and fixed in a different way in theouter sleeve 114 whereby it basically depends on which materials areused for the ring support.

According to FIG. 13 the outer sleeve 114 has on its inner circumferencea fixing groove 120 in which the disc-like flange 113 snap-fits whenpressed in. In order to reduce the sealing friction in the sealing liparea both the inner ring 112 and the outer sleeve are extended axiallyin the direction of the sealing lips of the seal 110 which thereby forma support 131 and 130 respectively.

According to FIG. 14 the outer sleeve 114 has windows 121 into which theprojections 122 on the disc-like flange 113 snap-fit.

In FIG. 15 the disc-like flange 113 is fixed on a ring-shaped stop 123in one direction whilst it is fastened additionally in the otherdirection by material imprinting 124.

In the embodiment according to FIG. 16 the outer sleeve 114 is made froma deformable material so that after fixing the disc-like flange 113 inthe outer sleeve 114 the latter is finally fastened by rolling 125. Theinner ring 112 and the disc-like flange 113 can be made from a differentmaterial and can be supported from inside during rolling. The inner ringbead 117 on the outer sleeve 114 can in this embodiment likewise be madefrom a different material e.g. from a plastics and for example appliedat a later date.

In the embodiment to FIG. 17 the outer sleeve 114 and the inner ring 112as well as the disc like flange 113 are made from deformable materialsuch as for example sheet steel wherein the outer sleeve 114 has a stopwhich can be made for example by rolling whereby the disc-like flange iswelded onto same. The ring bead 115 and the inner ring bead 117 are alsomade by flanging over the material.

In the embodiment according to FIG. 18 the disc-like flange 113 has acircular ring shaped extension 126 which corresponds with the innercircumference of the outer sleeve 114 whereby the projections 118 on theouter sleeve 114 reach through the openings in the circular ring shapedextension 126 and at the same time fix this extension.

In FIG. 18a a cut-out section of the overlapped area of the inner ring112 with the outer sleeve 114 is shown with an alternative fastening ofthese component parts. According to this a partial gap-free punched area132 is provided between the outer sleeve 114 and the circular ringshaped extension 126 of the inner ring 112 to form a radially inwardlydirected projection which engages by way of example in the installedstate in circumferential groove of the ring piston 108.

According to FIG. 19 the disc like flange 113 is fixed between a stop127 and the end face of the ring piston 108.

The disc like flange 114 can however also be fixed by a thread 128 onthe inner circumference of the outer sleeve and on the outercircumference of the disc like flange according to FIG. 20.

According to FIG. 21 the outer sleeve 114 has a solid flanged edge andforms an internal flange 129 on which the circular ring shaped flange isfastened, more particularly by welding or soldering.

In the embodiment according to FIG. 21 the seal is indeed supported onthe outer sleeve 114 but is not engaged from behind so that thefastening is produced by the ring bead 115.

The embodiment according to FIG. 22 corresponds substantially to theembodiment according to FIG. 18 but, as can be seen from the wallthickness other materials are selected and the circular ring shapedextension 126 is stuck to the inner circumference of the outer sleeve114.

The seal carrier 111 is in the embodiment according to FIG. 23 made froma similar material and constructed similar to FIG. 17 wherein the innerring 112 and the disc-like flange 113 as well as the outer sleeve 114are made from a deformable sheet steel plate and the disc-like flange113 adjoins and is welded to the stop 127 a, which is formed similar tothe stop 127 in FIG. 19. The outer sleeve 114 has in the embodimentaccording to FIG. 112 no projections 118 but a sunken rolled-in areawhich is likewise in active connection with an undercut section on thering piston.

As a further measure of reducing the wear on the ring piston 108 whenaxial vibrations appear, as an alternative to a drawn or flanged edgewhich engages with positive locking on the ring piston 108, FIG. 14shows groove rings 133 a, 133 b. One of the groove rings 133 a, 133 bshown in FIG. 14 is sufficient to secure the seal carrier 111 on thering piston 108, these groove rings being guided in corresponding ringgrooves of the outer sleeve 114 and the ring piston 108 and of thecircular ring shaped extension 126 and ring piston 108 respectively.

The seal carrier 111 according to FIG. 15 has in order to increase thestiffness a practically gap-free adaptation of the outer sleeve 114 andthe inner ring 112 to the seal 110. The outer sleeve 114 thereby extendsover a wide axial area and thus enclosed the seal 110 on the outside upto the shoulder of the outer sealing lip. To produce a prefitting unitit is possible to mount the seal 110 with the back of the seal first onthe disc like flange 113 of the inner ring 112 before these componentparts are enclosed concentrically by the outer sleeve 114. Anon-detachable connection between the inner ring 112 and the outersleeve 114 can then be produced for example by adhesive or soldering.Fixing the seal carrier 111 in position is achieved by means of aradially inwardly directed partial or circumferential edging 134 of theouter sleeve 114 which engages with positive locking for example in acircumferential groove of the ring piston 108.

In a further embodiment the seal 110 as a twin-component design isconnected non-detachably direct to the inner ring 112 and the outersleeve 114. The construction uses an inner ring 112 and outer sleeve 114made of plastics and able to be manufactured together with the seal 110in a two-phase injection moulding process. To secure these componentparts and increase the stiffness the outer sleeve 114 is enclosed by astrip 136 preferably made of sheet metal. A snap-fit nose 135 mounted inan axial extension of the outer sleeve 114 serves to fasten the unitcomprising the seal carrier 111 and seal 110 on the ring piston 108whereby in the installed state the nose engages with positive locking ina radial recess of the ring piston 108.

FIG. 27 shows a hydraulically operable release system 201. Thiscomprises a cylinder 202 formed as a slave cylinder wherein this ismounted concentric about a gearbox input shaft (not shown in FIG. 27)which connects an internal combustion engine to a shift transmission.The cylinder 202 is detachably fastened on a gearbox housing (likewisenot shown). The cylinder 202 has a pressure chamber 203 which is definedradially by a bore wall 204 and a guide sleeve 205. The guide sleeve 205is fastened through an end-side ring flange 206 on the cylinder 202 andis located in the installation position radially spaced from the borewall of the cylinder 202 and from the gearbox input shaft. The guidesleeve 205 which is made from steel plate is preferably made by adeep-drawing process without stock removal. The cylinder 202 representsa cast part for which aluminium in particular is suitable. A ring piston207 is guided axially displaceable in the pressure chamber 203 and isassociated on the pressure chamber side with a seal 208.

A seal carrier 209 in which the seal 208 is held with keyed engagementin a trapezoidal shaped mounting forming two undercut sections serves tofasten the seal 208 on the ring piston 207. With an outer axiallyaligned arm 210 the seal carrier 208 encloses an end area of the ringpiston 207 whereby the arm is provided at the end side with an edge 211directed radially inwards at right angles and engaging in the installedstate behind a shoulder 212 of the ring piston 207. The seal 208 isfurther provided with a radially inner sealing lip 213 which sealinglyadjoins a sleeve face 215 of the guide sleeve 205. A further radiallyouter sealing lip 214 is supported in sealing manner on the bore wall204 of the cylinder 202. At the end remote from the pressure chamber 203the ring piston 207 is provided with a release bearing 216 which in theinstalled state is supported with force-locking engagement on releasemeans of a shift and separate clutch connected to the internalcombustion engine. The pressure chamber 203 can be biased with hydraulicmeans through a supply bore 217 formed in the cylinder 202 to axiallydisplace the ring piston 207.

FIG. 28 shows the seal 208 according to the invention on an enlargedscale. According to this the geometric arrangement or formation of thesealing lips 213, 214 is asymmetric. The radially inner sealing lip 213thereby has a longitudinal extension, characterised by the measurementL₁, starting from a back 218 of the seal up to a function point 219 onthe outer contour of the sealing lip 213. A corresponding measurement L₃is provided for the radially outer sealing lip 218 which is set betweenthe back of the seal 218 and the function point 220. The function points219, 220 determine the point or zone with which the sealing lips 213,214 are supported with the greatest radial pretension on the sealingtrack of the bore wall 204 or guide sleeve 205. To produce a roundedtransition at the function points 219, 220 a radius R₁; R₂ is providedeach time. The installation space of the seal 208 between the cylinder202 or the bore wall 204 respectively and the guide sleeve 205,according to FIG. 27, is indicated in FIG. 28 by the measurement D₁.This installation measurement allocates to each sealing lip 213, 214 inthe non-installed state a so-called active line which intersects therelevant outer contour of the sealing lip 213, 214. The active linethereby forms each time an overlap zone A and an underlap zone B for thesealing lip 213 and correspondingly for the sealing lip 214 the overlapzone C and the underlap zone D. The overlap zones A;C are therebyrestricted starting from the intersection point of the active line withthe outer contour up to the function points 219,220. To explain theindividual zones these are shaded differently for each sealing lip. Theoverlap zones A,C are adjoined axially by a further axially aligned areaexceeding the active lines. These sections have a longitudinal extensionL₄ which in the non-installed state of the seal (8) form a cylindricalouter contour.

The seal 208 is provided on the end side with a circumferential V-shapedring groove 221 which forms a radius R₃ at the groove base. The groovedepth is determined by the measurement L₂ which extends between the back218 of the seal and the groove base. Furthermore the shape of the seal208 provides that the outer contour thereof is formed for the sealinglips 213, 214 at the transition to the back 218 of the seal rounded inthe form of a radius R₄;R₅. The wall thickness of the seals 213, 214 islikewise formed differently. As explained in FIG. 28 the measurement L₆of the sealing lip 214 exceeds the corresponding measurement L₅ of thesealing lip 213. This measurement comparison is produced each time by aright-angled arm extending from the outer contour of the ring groove 221and guided through the intersection point of the active line with theouter contour of the relevant sealing lip. To fasten the seal 208 in theseal carrier 209 according to FIG. 27 the back 218 of the seal isadjoined by an attachment 222 with a restriction on both sides whichfits with keyed engagement in the seal carrier 209. For the chemicalfinishing treatment of the seal 208 according to the invention it isproposed to bias the seal at least in part. For this it is suitable totreat the outer contour of the two sealing lips 213, 214 starting fromthe tangent point of the radii R₄; R₅ with the back 218 of the seal, upto the free end.

FIGS. 29 and 30 show the pedal forces required to operate the shift andseparate clutch between a release system of the previous construction(FIG. 29) and a release system according to the invention.

In both diagrams the pressure, i.e. the pipeline pressure (bar) isentered on the abscissa and the friction force (N) is entered on theordinate whereby the scales between the two diagrams are the same. FIG.30 shows the friction force reduced to about 90 N and which according toFIG. 29 amounts to about 400 N taking into account the same operatingpressures.

The patent claims filed with the application are proposed wordingswithout prejudice for obtaining wider patent protection. The applicantretains the right to claim further features disclosed up until now onlyin the description and/or drawings.

Reference used in the sub-claims refer to further designs of the subjectof the main claim through the features of each relevant sub-claim; theyare not to be regarded as dispensing with obtaining an independentsubject protection for the features of the sub-claims referred to.

The subjects of these sub-claims however also form independentinventions which have a design independent of the subjects of thepreceding claims.

The invention is also not restricted to the embodiments of thedescription. Rather numerous amendments and modifications are possiblewithin the scope of the invention, particularly those variations,elements and combinations and/or materials which are inventive forexample through combination or modification of individual features orelements or process steps contained in the drawings and described inconnection with the general description and embodiments and claims andwhich through combinable features lead to a new subject or to newprocess steps or sequence of process steps insofar as these refer tomanufacturing, test and work processes.

What is claimed is:
 1. Hydraulically operable release system for avehicle clutch located between an internal combustion engine and amanual shift transmission, comprising a slave cylinder concentricallysurrounding a drive shaft and having a circular annular pressure chamberin which a ring piston is axially displaceably guided and which isprovided, on the side facing the pressure chamber, with a seal which issecured on the piston by a circular ring shaped seal carrier, whereinthe seal has an undercut section and is fitted into the seal carriersubstantially without forming any interspaces.
 2. Hydraulically operablerelease system for a vehicle clutch located between an internalcombustion engine and a manual shift transmission, comprising a slavecylinder concentrically surrounding a drive shaft and having a circularannular pressure chamber in which a ring piston is axially displaceablyguided and which is provided, on the side facing the pressure chamber,with a seal which is secured on the piston by a circular ring shapedseal carrier, wherein the seal carrier: a) has in an end side radiallyspaced from the inner and outer diameter an opening which widensradially with increasing axial depth to form a trapezoidally undercutinternal profile; b) forms rounded lead-in zones in the area of theopening; c) is supported on an end face of the ring piston by a planarsurface opposite the opening; d) is fixed with axial play and radialplay on the ring piston by an outer axial projection enclosing an endarea of a sleeve face of the ring piston; e) is shaped without stockremoval from a sheet metal strip; f) has an inner projection which isguided up to the ring piston whilst maintaining an annular gap (Z₁, Z₂),wherein: a wall thickness S₁ on the outer projection is reduced in theremaining sections of the seal carrier; a transition between the endside and the outer and inner projection is rounded in such a way thatstarting from the end side a larger radius (R₂, R₄) adjoins an initiallysmaller radius (R₁, R₃) and the projection intersects each time as astraight line the transition formed by the radii (R₁, R₂, R₃, R₄); thetrapezoidally undercut internal profile has an overhang dimensionH>0.1S₁.
 3. Hydraulically operable release system for a vehicle clutchlocated between an internal combustion engine and a manual shifttransmission, comprising a slave cylinder concentrically surrounding adrive shaft and having a circular annular pressure chamber in which aring piston is axially displaceably guided and which is provided, on theside facing the pressure chamber, with a seal which is secured on thepiston by a circular ring shaped seal carrier, wherein the seal carrierhas in an end side radially spaced from the inner and outer diameter anopening which widens in the axial direction with increasing depth toform a trapezoidally undercut internal profile into which the seal isfitted without forming interspaces.
 4. Release system according to claim3, wherein the ring piston is provided at the end directed towards thepressure chamber with a shoulder protruding axially at the end face andguided up to a section of the seal carrier whilst maintaining an annulargap Z₂, Z₃.
 5. Release system according to claim 4, wherein the shoulderis guided from the ring piston up to the projection of the seal carrierwhilst maintaining the annular gap Z₂.
 6. Release system according toclaim 4, wherein a shoulder of the piston which is guided up to aradially aligned section of the seal carrier whilst maintaining theannular gap Z₃.
 7. Release system according to claim 3, wherein the sealcarrier has a planar surface opposite the opening supported on an endface of the ring piston.
 8. Release system according to claim 7, whereina measured distance L₁ of >3.5S₁ is provided between the end side andthe planar surface.
 9. Release system according to claim 7, wherein theseal carrier has an outer projection of an overall length L₂ exceeding alength L₁ which extends from an entry plane of the opening up to theplanar surface.
 10. Release system according to claim 7, wherein theseal carrier comprises an inner projection and the planar surface issitting flush against the end face of the ring piston whilst maintainingan annular gap Z₁ between the inner projection and the end face. 11.Release system according to claim 3, wherein the seal carrier formsrounded lead-in zones in an entry of the opening.
 12. Release systemaccording to claim 11, wherein the lead-in zone of the seal carrier isadjoined by a doubled area radially outside the lead-in zone. 13.Release system according to claim 12, wherein the measured distance L₁between the end side and the planar surface corresponds maximum to 3.5times the value of the wall thickness S₁.
 14. Release system accordingto claim 11, wherein in the rounded transition zone between the end sideand the axial projection starting from the end side an initially smallerradius (R₁, R₃) is adjoined by a larger radius (R₂, R₄).
 15. Releasesystem according to claim 11, wherein the lead-in zone has radii R₅, R₆greater than a wall thickness S₁ of the seal carrier.
 16. Release systemaccording to claim 11, wherein the lead-in zone has radii R₅, R₆ and thetrapezoidally undercut internal profile has radii R₇, R₈ starting fromthe planar surface that are less than or equal to the radii R₅, R₆. 17.Release system according to claim 11, wherein the seal carrier has anouter projection and a ventilation groove in at least one of the lead-inzones aligned axially parallel to the outer projection.
 18. Releasesystem according to claim 3, wherein the seal carrier is fixed withaxial play and radial play on the ring piston by an outer axialprojection enclosing an end area of a sleeve face of the ring piston.19. Release system according to claim 18, wherein a measurement of >0.2mm is provided for the wall thickness S₁ in the outer projection. 20.Release system according to claim 3, wherein a position of the axis ofsymmetry (Sa) of the inner profiled section is arranged coinciding withor off-set from the front end centre (M) of the seal carrier. 21.Release system according to claim 3, wherein a seal carrier having asymmetrically shaped internal profiled section which forms two radiallyopposite undercut sections.
 22. Release system according to claim 3,wherein that the seal carrier has an undercut section which is directedtowards the inner projection.
 23. Release system according to claim 3,wherein a seal carrier having an undercut section directed towards theouter projection.
 24. Release system according to claim 3, wherein aventilation bore is formed in the planar surface of the seal carrier.25. Release system according to claim 3, wherein the inner projectionhas a conical taper.
 26. Release system according to claim 3, whereinthe seal carrier is formed out of sheet metal stock without achip-removing machining operation.
 27. Release system according to claim3, wherein: the seal carrier has an inner projection extending close tothe ring piston but leaving an annular gap (Z₁, Z₂, Z₃) between theinner projection and the ring piston; the seal carrier has an outerprojection with a wall thickness S₁, while all other portions of theseal carrier have a wall thickness smaller than S₁; a transition betweenthe end side and the outer and inner projection is rounded in such a waythat starting from the end side a larger radius (R₂, R₄) adjoins aninitially smaller radius (R₁, R₃) and the projection intersects eachtime as a straight line the transition formed by the radii (R₁, R₂, R₃,R₄); a measurement H>0.1S₁ is provided for the radial overhang of thetrapezoidally undercut internal profile.
 28. Release system according toclaim 27, wherein the annular gap (Z₁, Z₂, Z₃) is greater than or equalto 0.1S₁.
 29. Release system according to claim 3, wherein a metalmaterial, capable of being deep-drawn is selected as the material forthe seal carrier.
 30. Release system according to claim 29, wherein themetal material is St4.